Method for identifying data encoded by PPM modulation, and receiver for said method

ABSTRACT

An identification method for a data Sk is disclosed which includes;
         a) construction of a chronological sequence {T 1 ; . . . ; Ti; . . . ; TN} of times of arrival Ti of pulses or a block of successive pulses,   b) calculation of a value of similarity between this sequence {T 1 ; . . . ; Ti; . . . ; TN} and a predetermined chronological sequence {TREFk 1 ; . . . ; TREFkj; . . . ; TREFkM} of times of arrival coding the data Sk for several time offsets Ol between the sequence {T 1 ; . . . ; Ti; . . . ; TN} and the sequence {TREFk 1 ; . . . ; TREFkj; . . . ; TREFkM},   c) identification of the data Sk in the series {T 1 ; . . . ; Ti; . . . ; TN} if the calculated value of similarity for one of the time offsets Ol exceeds a predetermined threshold.

This application is a continuation application of prior InternationalApplication No. PCT/EP2009/053471, filed on Mar. 24, 2009 and claimingpriority to European (EP) Patent Application No. 08102940.7, filed Mar.26, 2008.

TECHNICAL FIELD

The invention relates to a method of identifying a given data Sk whichis encoded by PPM modulation (Pulse Position Modulation) in a receivedsignal. The invention also relates to a receiver of such a signal.

PRIOR ART

In a PPM or time modulation of pulse positions, each pulse may be earlyor late compared to a known theoretical time of arrival in order toencode such data as, for example, a “0” or a “1”. In this description,the term “data” means any type of information, such as a transmitter ID,character, symbol, bit or other.

PPM modulation includes also particular PPM known by the term DPPMmodulation (Differential Pulse Position Modulation). In DPPM modulation,the differences between the times of arrival of pulses in a pulsesequence encode the data.

Specifically, when PPM modulation is used, all data transmitted isdefined by a sequence of M pulses or M pulse blocks, where M is aninteger which is strictly greater than one. M is not necessarily thesame for all the encoded data. The temporal arrangement of the M pulsesor M pulse blocks of the same sequence represents encoding of the data.The successive times Ti of arrival of these pulses or pulse blockstherefore encode the data transmitted. Each time of arrival Ti is anumerical value indicating a time elapsed since a common origin.

When the amplitudes of the pulses are large enough to allowdiscrimination of each of them from ambient noise, times Ti maycorrespond to the times of arrival of each pulse. In this case, the datais encoded by a sequence of M pulses. Conversely, when the amplitudes ofthe pulses are lower than the ambient noise, pulse blocks are sent. Thearrangement of the pulses within each of these blocks is predeterminedso that the receiver can easily identify each of these blocks. In thiscase, the times Ti correspond to the times of arrival of the pulseblocks and the data is encoded by M pulse blocks.

The PPM modulations are used in ultra-wideband technology better knownunder the term of UWB technology (Ultra Wide Band). Only by way ofillustration, the following description is made in this particularcontext.

The transmission of data by a UWB technology is carried out with a datasignal which includes a series of very short pulses without necessarilyusing a carrier frequency. The duration of these pulses can be less thanone nanosecond. As the data pulses are very short in the time domain, bytransformation into the frequency domain, one can lead to obtaining anultra-wide band spectrum, which defines UWB. The frequency spectrumranges from 500 MHz to several GHz. The frequency bandwidth is generallygreater than 25% as compared to the central frequency for a UWBtechnology.

The pulses can be of different shapes as long as their durations aregenerally less than one nanosecond. It could be, for example, composedof Gaussian pulses having one or two polarities or wavelets.

Generally, multiple ultra-wideband transmitters and receivers can benear each other. Thus, generally, the signals transmitted between atransmitter and a receiver must also contain a particular data calledhere the “transmitter ID,” which identifies the transmitter whichtransmitted the signal.

In addition, all codes used for encoding data are, in principle,orthogonal. This means that by correlating them to one another, theresult of the correlation gives a value close to zero.

Generally, when a PPM modulation is used, the clock of the receiver mustbe precisely synchronised to the clock of the transmitter in order toaccurately determine if a pulse is ahead or behind a theoretical time ofarrival. Such receiver clock synchronisation is often complex toachieve.

DISCLOSURE OF THE INVENTION

A main purpose of the invention disclosed herein consists in proposing amethod, which may not include a synchronization and, which may identifydata Sk encoded by PPM modulation in a received signal.

It thus concerns a method that may comprise:

-   -   a) construction of a chronological series {T1; . . . ; Ti; . . .        ; TN} of times of arrival Ti of successive pulses contained in a        received signal,    -   b) calculation of a value of similarity between this series {T1;        . . . ; Ti; . . . ; TN} and a predetermined chronological        sequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM} of times of        arrival coding the data Sk for several time offsets Ol between        the series {T1; . . . ; Ti; . . . ; TN} and the sequence        {TREFk1; . . . ; TREFkj;. . . ; TREFkM}, each value of        similarity being representative of the correlation between the        series {T1; . . . ; Ti; . . . ; TN} and the sequence {TREFk1; .        . . ; TREFkj; . . . ; TREFkM} for a given time offset Ol,    -   c) identification of the data Sk in the series {T1; . . . ; Ti;        . . . ; TN} if the value of similarity calculated for one of the        time offsets Ol exceeds a predetermined threshold.

Construction of the series {T1; . . . ; Ti; . . . ; TN} may not requirea time synchronisation between the clocks of the receiver and of thetransmitter. Furthermore, calculation of the value of similarity betweenthe series {T1; . . . ; Ti;. . . ; TN} and the sequence {TREFk1; . . . ;TREFkj; . . . ; TREFkM} for different time offsets may also not requirea synchronisation of the receiver and transmitter clocks. Therefore, byusing this method, the data Sk may be identified without the transmitterand receiver clocks being synchronised.

In addition, given that one calculates a value of similarity fordifferent possible time offsets, the data Sk may be identified only if apredetermined threshold is exceeded. Due to this, this method is robustagainst noise. In particular, this method is robust in the presence ofparasitic pulses in the received signal causing the appearance ofparasitic times in the series {T1; . . . ; Ti; . . . ; TN}. Suchparasitic pulses may for example be caused by multipath signals betweenthe transmitter and the receiver, or generated by other emitters ofelectromagnetic waves near the transmitter and the receiver.

The method above also limits the consequences of errors in measurementof times of arrival Ti. These errors may result in a measurement of atime Ti which is slightly ahead or behind the time when the pulse orblock of pulses has actually been received by the receiver. This erroris known as “jitter”.

The publication entitled “Low Complexity Synchronisation Algorithm forNon-Coherent UWB-IR Receivers”, published in the names of BenoîtMiscopein et al. at the occasion of the VEHICULAR TECHNOLOGY CONFERENCE,2007, VTC2007-SPRING, IEEE 65TH, IEEE, PI, pages 2344 to 2348 (ISBN:978-1-4244-0266-3), and patent application FR 2877169A, some inventorsof which have contributed to the above mentioned publication, disclosemethods of a similar kind to that which has been previously described,in which calculations of differences between times of arrival are usedto identify a signal. Each difference is calculated between twosuccessive times of arrival, thus allowing a decrease of the “jitter”influence in the identification method. Further solutions are suggestedin these documents to decrease even more the “jitter” influence, butsuch solutions imply a complexification of the processing going in theopposite direction of the present purpose, that is achieving asimplification of the identification method.

The method according to the present invention provides an alternatecalculation of the value of similarity which is not based on differencesbetween times of arrival for pairs of times (Ti, Tj). Indeed, when thevalue of the differences between times of arrival Ti and Tj is used, theerrors in the measurement of the times may add up and lead to anerroneous decision, even if these differences are solely calculatedbetween successive times of arrival.

Thus, the present method provides that each value of similarity iscomputed on the basis of the differences between time pairs (Ti;TREFkj).

Here, thanks to the use of the value of similarity, the errors in themeasurement of the times Ti cannot add up, as far as each time Ti istaken into account individually. This improves the robustness of thismethod with respect to the errors in the measurement of times Ti.

In the above method, only the times of arrival Ti of received pulses areused to identify the data Sk. The amplitude or polarity of the receivedpulses are not taken into account. This therefore allows easyidentification of any of the information emitted by a transmitterdistant from a receiver while another transmitter, much closer to thereceiver, emits parasitic pulses of much larger amplitudes.

Finally, the series {T1; . . . ; Ti; . . . ; TN} may solely containtimes of arrival. This series may therefore be easily registered in asmall amount of memory. This series may also be easily transmitted overan information transmission line of low bandwidth. Thus, the computationof this series may be easily relocated or moved or executed later.

The embodiments of this method may include one or more of the followingcharacteristics:

-   -   calculation of the value of similarity for a given time offset        includes:        -   counting the differences between the time pairs (Ti; TREFkj)            included in a range of values containing this time offset,            and        -   computation of the value of similarity from the result of            this count;    -   calculation of this value of similarity includes:        -   incrementation of a counter associated with this range of            values with a first predetermined step each time a            difference between the time pairs (Ti; TREFkj) occurs within            this range, and        -   incrementation of the same counter with a second            predetermined step each time a difference between the time            pairs (Ti; TREFkj) occurs within an adjacent range of            values, the second predetermined step being less than the            first predetermined step.    -   method includes:        -   calculation of the value of similarity for all possible time            offsets, and        -   computation of a global time of arrival TOAG for the data Sk            from the time offset for which the calculated value of            similarity is the highest;    -   method includes the determination of the distance between the        transmitter and the receiver or of the position of the        transmitter in relation to the receiver which received the        signal and also from the computed time TOAG;    -   method includes decoding of a data Dt which is encoded in the        received signal from the successive computed times TOAG;    -   data Sk is an identifier of the transmitter of the received        signal;    -   construction of the series {T1; . . . ; Ti; . . . ; TN}        includes:        -   calculation of a value of similitude between samples of the            received signal and a predetermined block of several pulses,        -   generation of a new time Ti indicating the time at which            this value of similitude has exceeded a predetermined            threshold;    -   method includes:        -   calculation of several values of similitude between the last            samples obtained and respective predetermined blocks of            several pulses, each predetermined block coding a respective            data Db, and        -   transmission of the data Db to a processing unit for this            data each time that the value of similitude associated to            this data exceeds a predetermined threshold;    -   method includes filtering the received signal as a function of        the identified Sk signal to eliminate the pulses or the blocks        of parasitic pulses not coding the data Sk.

Embodiments of the method according to the invention may further presentthe following benefits:

-   -   calculating the value of similarity from the differences between        time pairs (Ti; TREFkj) prevents an accumulation of errors in        measurement of times Ti;    -   calculating the value of similarity from the counting of        differences between time pairs (Ti; TREFkj) simplifies        calculation of such similarity value,    -   computation of the time TOAG from the different calculated        values of similarity allows calculating the time offset without        having to synchronise the clocks of the transmitter and of the        receiver,    -   determining the distance or position of the transmitter from the        computed time TOAG provides more accurate results,    -   coding additional data Dt using different successive computed        times TOAG allows decoding of this data Dt without a        synchronisation of the receiver and transmitter clocks being        necessary,    -   when data Sk is a transmitter identifier, the method allows        identifying this transmitter without synchronisation of the        receiver and transmitter clocks,    -   constructing each of the times Ti from a value of similitude        between the last obtained samples and a predetermined block of        pulses allows improvement of the signal to noise ratio,    -   using different predetermined pulse blocks allows coding of        additional data Db using these blocks.

The invention also relates to a receiver of a signal containing a PPM(Pulse Position Modulation) encoded data Sk in which the receiver mayinclude:

-   -   a constructor of a chronological series {T1; . . . ; Ti; . . . ;        TN} of times of arrival Ti of successive pulses or blocks of        pulses contained in the received signal,    -   a calculator capable of:        -   constructing a value of similarity between this series {T1;            . . . ; Ti; . . . ; TN} and a predetermined chronological            sequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM} of times            of arrival coding the data Sk for several time offsets Ol            between the series {T1; . . . ; Ti; . . . ; TN} and the            sequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM}, each            value of similarity being representative of the correlation            between the series {T1; . . . ; Ti; . . . ; TN} and the            sequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM} for a            given time offset Ol,        -   identifying data Sk in the series {T1; . . . ; Ti; . . . ;            TN} if the calculated value of similarity for the time            offset 01 exceeds a predetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better-understood by reading the description whichfollows, given solely by way of a non-limiting example and withreference to the drawings in which:

FIG. 1 is a schematic illustration of a receiver of a given PPM encodeddata Sk;

FIG. 2 is a schematic illustration of a calculator of similitude valuesused in the receiver in FIG. 1;

FIG. 3 is a flow chart of a method to identify the data Sk beingprocessed by the receiver in FIG. 1;

FIGS. 4 to 9 are schematic illustrations of different timing signalsprocessed by the receiver in FIG. 1;

FIG. 10 is a histogram showing the calculation of a value of similarity,and

FIGS. 11 and 12 are schematic illustrations of two other possibleembodiments of the receiver.

DETAILED DESCRIPTION

FIG. 1 shows a system 2 for transmitting signals between transmittersand receivers. For illustration purposes, system 2 uses UWB fortransmission of these signals.

To simplify FIG. 2, only two transmitters 4 and 6 were represented andone sole receiver 8.

The transmitters 4 and 6 are each able to transmit a sequence of pulsescoding respectively, one data S1 and S2 using PPM modulation. Here, oneconsiders that the data S1 and S2 are, respectively, identifiers fortransmitters 4 and 6. More precisely, the S1 and S2 data are encoded bythe times of arrival of a predetermined block of pulses. The S1 and S2data are noted as Sk, where k is an integer number which can take thevalue 1 or 2.

Here, this block of pulses is the same, the signal being eithertransmitted by transmitter 4 or 6. Each pulse in each block is less than5 ns, preferably less than 1 ns. A sequence comprises M predeterminedblocks of successive pulses. The value of M is not necessarily the samefor the sequence coding S1 as for that coding S2.

Moreover, each of these transmitters is able to encode a data Dt, byusing DPPM modulation between the global times of arrival (TOAG) of thesequences coding the data S1 or S2.

The receiver 8 is furnished with a UWB antenna 10. This antenna islinked to a block 12 which allows executing different analogue methodson the received signal which are necessary to allow a conversion of areceived analogue signal into a digital signal. The output of block 12is connected to the input of an analogue-digital converter 14. Theperiod Te of sampling of the converter 14 is chosen to be less than halfthe duration of a pulse and, preferably, at least ten times less thanthe duration of a pulse contained in the received signal.

An output of the converter 14 delivers the received, sampled signal toan input of a constructor 16 of a series {T1; . . . ; Ti; . . . ; TN} oftimes of arrival Ti of pulse blocks contained in the received signal.

For example, in relation to this, the constructor 16 includes acalculator 18 of a value of similitude between the last samples of thereceived signal and the predetermined block of pulses. For example, thelast received samples correspond to those taken over a period of thereceived signal which lasts longer than the pulse block and shorter thantwo blocks of pulses. This calculator 18 is described in more detail inregards to FIG. 2.

The calculator 18 delivers, to an output, a value of similitude betweenthe last received samples and the predetermined block of pulses. Themore the correlation between the signal received and this predeterminedblock of pulses is important, the greater this value of similitude.

This output from the calculator 18 is connected to the input of acomparator 20. The comparator 20 constantly compares the value ofsimilitude to a predetermined threshold L1. At the time where this valueof similitude exceeds threshold L1, the comparator 20 generates a pulseleading edge on a signal transmitted to the input of a time-digitalconverter 22. This converter 22 is better known as a “Time to DigitalConverter.” The converter 22 generates, for each pulse leading edgereceived at its input, a numerical value corresponding to the time Ti atwhich the pulse edge is produced. In this way, the constructor 16delivers a chronological series of times of arrival Ti. The series of Ntimes Ti constructed during one sequence is noted {Ti; . . . ; Ti; . . .; TN}. N does not necessarily have the same value as M (number of pulseblocks in a sequence). For example, the series {T1; . . . ; Ti; . . . ;TN} can include supplemental parasitic times.

The output of the converter 22 is connected to an input of a calculator26 of values of similarity between the series {T1; . . . ; Ti; . . . ;TN} and a predetermined sequence SREFk of times of arrival. The SREFksequence solely contains the theoretical times of arrival of the pulsescoding the data Sk. These theoretical times are noted as TREFkj and theSREFk sequence can also be written in the form {TREFk1; . . . ; TREFkj;. . . ; TREFkM}. Each SREFk sequence therefore characterises a data Skwhich can be received by the receiver. These sequences arepre-registered in a memory 30 connected to calculator 26. Here, thememory 30 contains at least the sequences SREF1 and SREF2, respectivelycoding the data S1 and S2.

The value of similarity is representative of the correlation between theseries {T1; . . . ; Ti; . . . ; TN} and the SREFk sequence. Here, themore the correlation between the series and the sequence is important,the larger this value of similarity.

In order to carry out this task, the calculator 26 is also equipped witha buffer memory 28 which can store the series {T1; . . . ; Ti; . . . ;TN}.

The calculator 26 is connected by its output to a decoder 32 and to acalculating unit 34 of the distance between the receiver 8 and thetransmitters 4 and 6 or of the position of these transmitters 4 and 6.Here, the unit 34 is an external unit situated outside receiver 8.

Decoder 32 is able to decode the data Dt.

FIG. 2 represents a specific embodiment of similitude calculator 18.Here, this similitude calculator is implemented in the form of a filteradapted to the predetermined block of pulses. More specifically, this isa finite pulse response filter, better known under the term FIR (FiniteImpulse Response).

For example, the calculator 18 includes a delay line 40 composed of asuccession of blocks 41 to 49 which are each able to delay for asampling period Te the sampled signal received by the input of this line40. The blocks 41 to 49 are for example bascules D.

Here, the number of blocks in the line 40 was limited to nine only tosimplify the illustration.

The input and output of each of these blocks 41 to 49 are connected viarespective multipliers 62 to 71 to an adder 74. Each of the multipliers62 to 71 is able to multiply the input signal by a coefficient,respectively a0 to a9. The coefficients a0 to a9 are chosen according tothe predetermined block of pulses such that the received signal samplesare added to each other in a constructive way in the adder 74 only whenthe received signal contains a block of pulses identical to thepredetermined pulse block.

Thus, the output of the adder 74 is a value of similarity. This value isonly important if the last samples of the received signal correspond tothe predetermined pulse block.

The function of the receiver of system 2 will now be described in moredetail in regards to the method shown on FIG. 3 with the aid of timingdiagrams in FIGS. 4 to 8.

Initially, at a step 80, the transmitters 4 and 6 each send a signal tothe receiver 8 using UWB technology.

Here, in the remainder of this description, one deals only with thesignal sent by transmitter 4. The processing of the signal sent bytransmitter 6 can be inferred from the explanations given in relation tothe signal sent by transmitter 4.

Here, transmitter 4 sends pulse sequences. Each of these pulse sequencesencodes the data S1 by PPM modulation. Moreover, the transmitter 4encodes the data Dt by modulating the global times of arrival (TOAG) ofthe sequences.

FIG. 4 represents an illustration of a sequence of pulses transmitted bythe transmitter 4 in the particular case where this sequence is composedof three identical pulse blocks P1, P2 and P3. For example, each blockis formed by the repetition of the same pulse. Here, the pulse isrepeated three times in each block.

Moreover, in FIG. 4, there is a representation of a parasitic block ofpulses A1. This parasitic block is identical to blocks P1, P2 and P3,but time offseted in reference to these blocks. For example, block A1 isgenerated by a reflection of the signal transmitted on an obstacle or byanother user using the same block.

During stage 82, the signal transmitted by the transmitter 4 is receivedand captured by the antenna 10, of the receiver 8. Then, it traversesthe block 12 before being sampled by the converter 14.

During stage 84, the constructor 16 constructs from the sampled receivedsignal the series {T1; . . . ; Ti; . . . ; TN}. More precisely, duringan operation 86, the calculator 18 calculates the value of similitudebetween the last received samples and the predetermined block of pulses.Here, the predetermined pulse block corresponds to one of the blocks P1,P2 and P3 represented in the FIG. 4. More precisely, the samples arereceived in the delay line 40. At each sampling period, the samplescontained in the delay line are offseted by one block to the right andthe adder 74 carries out the addition of these samples after they havebeen multiplied by the coefficients a0 to a9. Thus, at each samplingperiod Te, the result of this addition, that is, the value of similitudeis delivered to the input of the comparator 20.

As shown by a plus sign 88 between FIGS. 4 and 5, the calculator 18carries out a type of addition of pulses of the pulse block P1 toconstruct a single increased amplitude pulse also designated by themarker P1 in FIG. 5.

Then, during an operation 89, each time the comparator 20 detects thatthe value of similarity exceeds the threshold L1, it generates a pulseleading edge on an output signal. This output signal is illustrated inFIG. 6.

Then, during an operation 90, the converter 22 converts each pulseleading edge to a numerical value Ti which is transmitted to thecalculator 26.

Here, each time Ti represents the time of arrival of a block of pulses.

Thus, the constructor 16 constructs the series {T1; . . . ; Ti; . . . ;TN}. In the example shown in FIG. 6, this series includes only fourtimes T1 to T4 among which time T3 is a parasitical time.

Next, the calculator 26 carries out a first step 94 of decoding of thisseries {T1; . . . ; T4}.

At the beginning of step 94, during an operation 96, the calculator 26calculates the values of similarity between the series {Ti; . . . ; T4}and the sequence SREF1 for different time offsets Ol. For example, thesequence SREF1 includes solely three times of arrival and is written{TREF11; . . . ; TREF13}. The sequence SREF1 is illustrated in FIG. 7.This sequence contains the theoretical times of arrival of the pulseblocks P1 to P3 coding the S1 data.

To calculate these values of similarity, the calculator 26 calculatesall the differences between the pairs (Ti; TREF1j). For example, here,the calculator 26 calculates the following differences:T1−TREF 11=−2T1−TREF12=−11T1−TREF13=−19T2−TREF11=7T2−TREF12=−2T2−TREF13=−10T3−TREF11=10T3−TREF12=1T3−TREF13=−7T4−TREF11=15T4−TREF12=6T4−TREF13=−2

Here, the numbers given above represent the durations of the timeintervals separating the time pairs (Ti; Tj) expressed as a number ofthe sampling period Te.

Then, a histogram of the different difference values obtained may bebuilt. This histogram is represented in FIG. 10 and corresponds to thenumbers given above.

Each time that the difference value takes a given value, a countercorresponding to that given value is incremented by a predeterminedstep. Here, the predetermined step is chosen to be equal to one.Moreover, to make the method more robust in regards to “jitter,” onealso increments by a lower predetermined step, the counters associatedto the values immediately inferior and superior to the given value. Forexample, the inferior step is equal to 0.5.

For example, the counter associated to the value “−2” is incremented bythree because the difference “−2” appears three times. One alsoincrements by 1.5 the counters associated to the values “−3” and “−1”.

At the same time, the counter associated to the value “−19” isincremented only by one because the value “−19” only appears once, andthe counters associated to the values “−20” and “−18” are onlyincremented by 0.5.

In the histogram in FIG. 10, each counter corresponds to a possible timeoffset Ol between the series {T1; . . . ; T4} and the sequence SREF1.The value of each counter corresponds to the value of similarity betweenthe series {T1; . . . ; T4} and the sequence SREF1 for the time offsetOl associated with this counter.

Then, during an operation 100, each value of similarity is compared to apredetermined threshold L2 (see FIG. 10). If the threshold L2 is notexceeded by any value of similarity, the method returns to operation 96to calculate this time the values of similarity between the series {T1;. . . ; T4} and the sequence SREF2 coding the S2 data. An example ofsequence SREF2 is represented in FIG. 8. In this other reference series,the instants TREF21 to TREF24 correspond to the arrival times of thepulse blocks coding the data S2.

In the case where the threshold L2 is exceeded by one of the values ofsimilarity calculated during the operation 98, then the calculator 26,during an operation 102, identifies the presence of the data Sk in theseries {T1; . . . ; T4}.

Moreover, during the operation 102, the calculator 26 selects the timeoffset Ol associated with the largest value of similarity. For example,in the example shown in FIG. 10, during step 102, the calculator 26selects the time offset “−2”.

Then, the overall time of arrival TOAG of the sequence S1 is determinedfrom the time offset Ol. For example, the time TOAG is taken as equal tothe time offset Ol associated with the largest value of similarity.

During an operation 104, the calculator 26 transmits the time TOAG todecoder 32 and to unit 34.

In parallel to operation 104, during an operation 106, the calculator 26also transmits the identified data S1 to the decoder 32.

During step 108, from the different times TOAG transmitted by thecalculator 26 and the data Sk associated with each of these times, thedecoder 8 decodes the data Dt contained in the signal transmitted by thetransmitter 4.

In parallel, during a step 110, unit 34 determines the position oftransmitter 4 from the times TOAG transmitted by the receiver 8 as wellas by other receivers situated near the transmitter 4. Unit 34 is alsoable to determine the distance which separates the receiver 8 from thetransmitter 4 from the different times TOAG delivered by the receiver 8.For this, conventional algorithms can be used. Eventually, in order toestimate the distance between the transmitter and the receiver, asynchronisation between the transmitter and receiver is required inaddition to the knowledge of the time TOAG. Also, to estimate theposition of a transmitter, a synchronisation between the receivers couldbe necessary.

FIG. 11 shows a system 120 for transmitting information betweentransmitters and receivers. In FIG. 11, only transmitters 122 and 124and a receiver 126 are represented. This system 120 differs from system2 in that the identifying data of the transmitters 122 and 124 isencoded in each pulse block. Thus, the arrangement of the pulses in theblock of pulses B1 transmitted by the transmitter 122 identifies thistransmitter. It is the same for the block of pulses B2 transmitted bythe transmitter 124. Since the transmitters 122 and 124 can beidentified by their respective block of pulses, it is no longernecessary for the data Sk to also identify these transmitters. In thisembodiment, the data S1 and S2 correspond therefore to anotherinformation than the identifying data of the signal transmitter.

The receiver 126 is identical to the receiver 8 except for the fact thatit includes an additional constructor 128 connected to the input of thesupplemental calculator 130 of values of similarity.

The constructor 128 is identical to the constructor 16 except for thefact that the calculator 18 is replaced by a calculator 130. Thecalculator 130 is, for example, a suitable filter. However, in the caseof the calculator 130, this filter is adapted to block B2. In contrast,the filter of the calculator 18 is adapted to block B1.

Thus, the constructor 16 solely constructs the series of times ofarrival for the B1 block of pulses, while the constructor 128 constructssolely the series of the times of arrival for the B2 blocks of pulses.

The calculator 130 is identical to calculator 26 except that itprocesses the series of times of arrival of B2 pulse blocks.

In this embodiment, the decoder 32 can be omitted. Indeed, decoding ofthe data Sk is directly carried out by the calculators 26 and 130.

FIG. 12 shows a system 140 for transmitting information betweentransmitters and receivers. To simplify the figure, only twotransmitters, 142 and 144, and a receiver 146 were represented.

In this embodiment, the identifying data S1 and S2 of transmitters 142and 144 are encoded in each pulse sequence by PPM modulation. Moreover,a data Dk is also encoded in each sequence in using for this purpose theamplitude or the polarity of the sequence pulses. No data is encoded inthe pulse blocks.

The receiver 146 is identical to the receiver 8 except that theconstructor 16 is replaced by a constructor 147. The constructor 147 isidentical to the constructor 16 except that the output of the calculator18 is also directly connected to a decoder 148.

One recalls that an example of the signal generated at the output ofcalculator 18 is represented in FIG. 5. At this place, the signalgenerated by the calculator 18 still includes the information on theamplitude or the polarity of each of the pulses transmitted by thetransmitter.

The decoder 148 receives the signal generated by the calculator 18, thedata Sk identified by the calculator 26 is the time TOAG selected by thecalculator 26.

The decoder 148 includes here a filter 150 able to eliminate parasiticpulses present in the signal generated by the calculator 18 on the basisof the data Sk and the time TOAG. For example, for this purpose, thefilter 150 uses the data Sk to identify a mask including time windowssituated solely at the places where the P1 to P3 pulses must bereceived. This mask is synchronised in relation to the signal generatedby the calculator 18 in using to this purpose the time TOAG. Any pulseincluded in the signal generated by the calculator 18 which is situatedoutside one of these time windows is eliminated. Thus, as represented inFIG. 9, this filter allows eliminating the parasitic Al pulse. Then, thedecoder 148 decodes the data Dk contained in the signal filtered by thefilter 150. This decoding of the encoded data Dk in amplitude or inpolarity is conventional.

Many other embodiments are possible. For example, other embodiments ofthe similitude calculator are possible. For example, the methoddescribed in the patent application EP 1 553 426 can be used to identifythe time of arrival for a block of pulses. The calculator of similitudevalues can also carry out a conventional correlation between thereceived signal and the predetermined block of pulses.

The calculation of similitude can also be carried out on the receivedanalogue signal. Thus, the analogue-digital converter can be omitted.

If the amplitude of each pulse is sufficient to exceed the amplitude ofnoise, then the times of arrival Ti correspond to the times of arrivalfor each pulse. In this case, the similitude calculator can be omitted.

Many other embodiments of the calculator of values of similarity arealso possible. For example, the counter associated with a time offset isincremented not as the value of the difference between the pairs oftimes (Ti; TREFkj) is equal to this time offset, but as soon as thedifference is included in a predetermined range of values containingthis time offset. In this embodiment, the counters associated with theadjacent ranges can also be incremented by a lower determined step.Preferably, in this embodiment, the range of values is strictly greaterthan the duration of a pulse. The size of the range of values willhowever be less than half the smallest time interval separating twopulse blocks.

The value of similarity can be calculated each time that a new time Tiis received. This value of similarity can also be calculated at aregular interval, for example, each millisecond. Typically, the regularinterval is chosen to be greater than the duration of reception of thedata Sk and preferably greater than two times the reception duration ofthe data Sk.

The time TOAG can be determined from the mean value of the times Ti orby adding the different times Ti or from the median of the times Ti.

The data can be encoded in a large number of different ways in thereceived signal. For example, a data Dk and the identifier of thetransmitter can simultaneously be encoded within the same sequence byPPM modulation. In this case, for each transmitter, the memory 30contains two reference sequences SREF11 and SREF12. The sequence SREF11corresponds to a sequence transmitted by this transmitter and coding afirst value of the data Dk. The sequence SREF12 also corresponds to aseries of characteristic times of the same transmitter but coding asecond value of the data Dk. In this case, while the calculator 26assesses that the value of similarity between the series {T1; . . . ;Ti; . . . ; TN} and the sequence SREF11 exceeds the threshold L2, thiscorresponds to the simultaneous decoding of the two followinginformation:

-   -   the identity of the transmitter, and    -   the encoded value of the data Dk.

In this embodiment, the decoder can be omitted.

Data other than the identifier of the transmitter can also be encodedwithin each pulse block. The coding of these data in each block can becarried out using a PPM modulation or using a modulation of amplitude orpolarity. In this case, the decoding of the data Db encoded in eachblock is carried out by the calculator of the value of similitude.

The decoder 32 can be omitted if only the data Sk must be decoded.

As an alternate embodiment, the positioning unit can be incorporatedwithin the receiver.

Conversely, the value of similarity calculator can be moved and placedoutside the receiver. This is made possible by the fact that the series{T1; . . . ; Ti; . . . ; TN} can be transmitted remotely by using a lowbandwidth. Indeed, in this series, the information relating to amplitudeor polarity of the pulses was omitted.

What has been described above applies to technologies other than UWBtechnology. For example, the identification method for the symbol Sk canbe applied to information transmission systems using CDMA technology oroptical transmission systems.

What is claimed is:
 1. A method for identifying a data Sk encoded by PPMmodulation (Pulse Position Modulation) in a received signal, said methodcomprising: a) construction of a chronological series {T1; . . . ; Ti; .. . ; Tn} of times of arrival Ti of successive pulses or blocks ofpulses contained in said received signal, b) calculation of a value ofsimilarity between said series {T1; . . . ; Ti; . . . ; TN} and apredetermined chronological sequence {TREFk1; . . . ; TREFkj; . . . ;TREFkM} of times of arrival coding said data Sk for several time offsetsOl between said series [T1; . . . ; Ti; . . . ; TN} and said sequence{TREFk1; . . . ; TREFkj; . . . ; TREFkM}, each value of similarity beingbased on differences between time pairs (Ti; TREFkj) so as to berepresentative of a correlation between said series {T1; . . . ; Ti; . .. ; TN} and said sequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM} for agiven time offset Ol, c) identification of said data Sk in said series{T1; . . . ; Ti; . . . ; TN} if said calculated value of similarity forone of said time offsets Ol exceeds a predetermined threshold, whereinsaid calculation of said value of similarity for a given time offsetincludes: counting differences between time pairs (Ti; TREFkj) which areincluded in a range of values containing said time offset, andcomputation of said value of similarity from a result of said countingstep.
 2. The method of claim 1, in which calculating said value ofsimilarity comprises: incrementation of a counter associated with saidrange of values with a first predetermined step each time a differencebetween said time pairs (Ti; TREFkj) falls within said range, andincrementation of said counter with a second predetermined step eachtime a difference between said time pairs (Ti; TREFkj) falls within anadjacent range of values, said second predetermined step being less thansaid first predetermined step.
 3. The method of claim 1, comprising:calculation of said value of similarity for all possible time offsets,and computation of a global time of arrival TOAG for the data Sk basedon the time offset for which the calculated value of similarity is thehighest.
 4. The method of claim 1, in which said data Sk is anidentifier of a transmitter of said received signal.
 5. The method ofclaim 1, in which construction of the series {T1; . . . ; Ti; . . . ;TN} comprises: calculation of a similitude value between samples of saidreceived signal and a predetermined block of several pulses, generationof a new time Ti indicating time at which said similitude value hasexceeded a predetermined threshold.
 6. The method of claim 1, includingfiltering said received signal as a function of said identified data Skto eliminate parasitic pulses or blocks of pulses not coding said dataSk.
 7. The method of claim 1, in which said data Sk is an identifier ofa transmitter of said received signal.
 8. The method of claim 1, inwhich construction of the series {T1; . . . ; Ti; . . . ; TN} comprises:calculation of a similitude value between samples of said receivedsignal and a predetermined block of several pulses, generation of a newtime Ti indicating time at which said similitude value has exceeded apredetermined threshold.
 9. The method of claim 1, including filteringsaid received signal as a function of said identified data Sk toeliminate parasitic pulses or blocks of pulses not coding said data Sk.10. The method of claim 2, including determination of a distance betweensaid transmitter and said receiver or of a position of said transmitterin relation to a receiver which received said signal and also from saidcomputed time TOAG.
 11. The method of claim 2, comprising: calculationof said value of similarity for all possible time offsets, andcomputation of a global time of arrival TOAG for the data Sk based onthe time offset for which the calculated value of similarity is thehighest.
 12. The method of claim 3, including determination of adistance between said transmitter and said receiver or of a position ofsaid transmitter in relation to a receiver which received said signaland also from said computer time TOAG.
 13. The method of claim 3,including decoding of a data Dt encoded in said received signal fromsuccessive computer times TOAG.
 14. The method of claim 3, in which saiddata Sk is an identifier of a transmitter of said received signal. 15.The method of claim 5, comprising: calculation of several similitudevalues between last samples of said received signal and respectivepredetermined blocks of several pulses, each predetermined block codinga respective data Db, and transmission of data Db to a processing unitof said data each time that said similitude value associated to saiddata exceeds a predetermined threshold.
 16. A receiver of a signalcontaining a data Sk encoded by a PPM modulation, said receivercomprising: a constructor of a chronological series {T1; . . . ; Ti; . .. ; TN} times of arrival Ti of successive pulses or blocks of pulsescontained in said received signal, a calculator capable of: constructinga value of similarity between said series {T1; . . . ; Ti; . . . ; TN}and a predetermined chronological sequence {TREFk1; . . . ; TREFkj; . .. ; TREFkm} of times of arrival coding said data Sk for several timeoffsets Ol between said series {T1; . . . ; Ti; . . . ; TN} and saidsequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM}, each value ofsimilarity being based on differences between time pairs (Ti; TREFkj) soas to be representative of a correlation between said series {T1; . . .; Ti; . . . ; TN} and said sequence {TREFk1; . . . ; TREFkj; . . . ;TREFkM} for a given time offset Ol, identifying said data Sk in saidseries {T1; . . . ; Ti; . . . ; TN} if said calculated value ofsimilarity for one of said time offsets Ol exceeds a predeterminedthreshold, wherein said constructing of said value of similarity for agiven time offset includes: counting differences between time pairs (Ti;TREFkj) which are included in a range of values containing said timeoffset, and computation of said value of similarity from a result ofsaid counting step.
 17. The method of claim 1, comprising: calculationof said value of similarity for all possible time offsets, andcomputation of a global time of arrival TOAG for the data SK based onthe time offset for which the calculated value of similarity is thehighest.
 18. The method of claim 17, including determination of adistance between said transmitter and said receiver or of a position ofsaid transmitter in relation to a receiver which received said signaland also from said computed time TOAG.
 19. The method of claim 17,including decoding of a data Dt encoded in said received signal fromsuccessive computed times TOAG.
 20. A method for identifying a data Skencoded by PPM modulation (Pulse Position Modulation) in a receivedsignal, said method comprising: a) construction of a chronologicalseries {T1; . . . ; Ti; . . . ; Tn} of times of arrival Ti of successivepulses or blocks of pulses contained in said received signal, b)calculation of a value of similarity between said series {T1; . . . ;Ti; . . . ; TN} and a predetermined chronological sequence {TREFk1 ; . .. ; TREFkj; . . . ; TREFkM} of times of arrival coding said data Sk forseveral time offsets Ol between said series [T1; . . . ; Ti; . . . ; TN}and said sequence {TREFk1; . . . ; TREFkj; . . . ; TREFkM}, each valueof similarity being based on differences between time pairs (Ti; TREFkj)so as to be representative of a correlation between said series {T1; . .. ; Ti; . . . ; TN} and said sequence {TREFk1; . . . ; TREFkj; . . . ;TREFkM} for a given time offset Ol, c) identification of said data Sk insaid series {T1; . . . ; Ti; . . . ; TN} if said calculated value ofsimilarity for one of said time offsets Ol exceeds a predeterminedthreshold d) calculation of said value of similarity for all possibletime offsets, and e) computation of a global time of arrival TOAG forthe data Sk based on the time offset for which the calculated value ofsimilarity is the highest.